MSI Motherboard installation problem - rebooting

Hi! My motherboard packed up so I bought another, this being a MSI 865GM3-LS. This is a P4 board, as was the old one, and we have 512mb RAM and 2.8GHz CPU. The machine is otherwise an eMachines PC, as bought from PC World. When I try to restart the computer it simply gets so far and then reboots every time (with Win XP) and I am told that I need to reinstall Windows to sort it out. Is this really right? Do I have to lose all the data on the hard disk? Or are there some files that I could copy across and make it work?
Any help appreciated!
Edward

if its a different motherboard but same cpu yes you have to reinstall windows but run a repair instead of a clean install.

So I take it that will keep my data?

yup

Fantastic, thanks!! Now up and running again at full speed, I was using an old PC. I couldn't do it from the original CD's that came with the computer but borrowed an XP CD from a friend which worked a treat, although took much longer than I expected - I thought it was a 10min job! Took about 1 hour! But working now so all is great, thanks a lot!
Edward

glad you got it running smoothly.